The present invention relates to the energy measurements performed in mobile radiocommunication systems.
Such measurements are usable in particular in radio link control procedures which serve in a general manner to optimize the quality of the transmissions and to minimize the interference between users. Among these procedures mention may be made of the regulating of transmission power by the mobiles and/or by the infrastructure, the handover control in cellular networks, the adaptation of the channel coding to the propagation conditions, the adaptation of the source coding (in particular the case of variable rate speech encoders of AMR “Adaptive Multi-Rate” type), the link adaptation procedures, etc.
The efficiency of this kind of procedure depends on the availability of reliable energy measurements within as short a timespan as possible, so that suitable decisions can be taken fairly quickly.
Moreover, allowance for point-like measurement samples may disturb the control algorithms implemented, by reason of the short-term fluctuations of the propagation channel. This is why time smoothing of these samples is generally performed by means of an averaging window of duration equal to N times the period between samples. The window may be rectangular: an arithmetic average of the last N samples is then computed. It is common to employ an exponential window with a forgetting factor α=1/N: upon receipt of an n-th sample C(n), a smoothed value C(n)=(1−α). C(n−1)+α·C(n) is then produced.
A long duration of the averaging window decreases the standard deviation of the estimate of the measured parameter, and therefore improves the reliability of the measurement. Conversely, a short duration increases the speed of acquisition of the measurements and therefore makes it possible, to the extent that they are reliable, to optimize the performance of the control algorithm which utilizes them. The choice of this duration results from a compromise between these two contradictory requirements.
An object of the present invention is to propose a finer way of making this compromise.